FIX: fix xlrd version; xlsx support was removed

setup.py

@@ -156,7 +156,7 @@ def setup_package():
         author_email='h.tomwoerden@indiscale.com',
         install_requires=["caosdb>=0.4.0",
                           "openpyxl>=3.0.0",
-                          "xlrd>=1.2.0",
+                          "xlrd==1.2.0",
                           ],
         packages=find_packages('src'),
         package_dir={'': 'src'},

tox.ini

 [tox]
-envlist=py36, py37, py38
+envlist=py36, py37, py38, py39
 skip_missing_interpreters = true
 [testenv]
 deps=nose
@@ -8,5 +8,5 @@ deps=nose
     pytest
     pytest-cov
     openpyxl
-    xlrd
+    xlrd == 1.2
 commands=py.test --cov=caosadvancedtools -vv {posargs}